The present invention relates to a fuel injector according to the species of claim 1, and to a method according to the species of claim 9, for the actuation of a fuel injector.
The closing times of fuel injectors are lengthened, on the one hand, by the adhesion forces between the armature and the core and, on the other hand, by eddy currents. To decrease the delay, it is known to cause a current to flow through the solenoid coil in the reverse direction in response to ending the current pulse that excites the fuel injector, in order to accelerate the decay of the residual field. Designing appropriate control elements is difficult and also yields only slight improvements in the closing times.
Another possibility is seen in building up one magnetic field for opening the fuel injector and building up a second magnetic field to hold the fuel injector in its open position. The strength of the holding field can then be selected so as to be so small that the eddy currents are small after the holding field is switched off.
From German Patent 23 06 007 C3, an electromagnetically actuatable fuel injector is known for injecting fuel into an internal combustion engine, in which the solenoid coil has three windings, which are driven by three separate circuits. In this context, the first circuit acts to rapidly open the fuel injector, the second circuit to keep the fuel injector open, and the third to generate a demagnetizing field that extinguishes the residual magnetic field, for rapidly closing the fuel injector.
One disadvantage in the fuel injector known from German Patent 23 06 007 C3 is that it is very expensive to manufacture an arrangement that has three circuits, which drive the three windings of the solenoid coil.
In addition, the spray-discharged fuel quantity per time unit is always identical, so that the metering of smaller fuel quantities in the lower rotational speed range of the internal combustion engine must be realized through a significantly shortened closing time and therefore through more powerful resetting springs and necessarily increased drive outputs of the solenoid coils. This places stress on the electrical components.
In contrast, the fuel injector according to the present invention having the features of claim 1, and the method according to the present invention having the features of claim 9, have the advantage that the metered fuel quantity per time unit can be switched over as a function of the rotational speed, because two switch positions are available, which can be driven individually in a selective manner, as a result of the alternating supply of current to two solenoid coils that cooperate with two armatures.
In this context, one advantage for the opening dynamics is especially the installation of a limit stop body, which, depending on the supply of current to the solenoid coils, either takes the second armature with it in the opening direction or strikes against the second anchor that is held fixed in place.
As a result of the measures indicated in the subclaims, advantageous refinements and improvements of the fuel injector described in claim 1, are possible.
Especially advantageous are the high closing dynamics, caused by the active switching back of the fuel injector from the opened to the closed state, the closing dynamics making possible very short closing times from both switch positions.
As a consequence of the closely-fitting dimensioning of the two working gaps, the fuel injector can achieve the desired injection properties for each switch position.
The first switch position having a small cross-sectional opening is especially advantageous in the lower rotational speed range, because small fuel quantities can be metered.
Also advantageous is the possibility of being able to switch from the lower switch position directly to the upper switch position.